The present invention relates to a method for mechanically foaming silicone compositions and more particularly the present invention relates to mechanically foaming silicone compositions by beating air into them and allowing them to cure under a vacuum.
All of such compositions that are contemplated by the present invention are quick curing. That is they will gel or set up at a period of time varying from a few seconds to not more than 15 minutes. There are various types of silicone compositions.
One type of silicone composition is an SiH olefin platinum catalyzed composition which comprises as the basic ingredients a vinyl polysiloxane, a hydride polysiloxane cross-linking agent and a platinum curing catalyst. An example such a composition for instance is to be found in Modic U.S. Pat. No. 3,436,366 which is hereby incorporated by reference.
Another type of silicone composition which cures to silicone elastomer is what is known as a room temperature vulcanizable (hereinafter referred to as RTV) silicone composition in which the basic components of the composition in the case of the two-component composition comprises a silanol end-stopped polymer, an alkyl silicate cross-linking agent, and a metal salt as the curing promoter. Usually the alkyl silicate is packaged separately from the silanol polymer and when it is desired to cure the composition the two components are mixed and allow to stand at room temperature whereupon they cure to a silicone elastomer. An example of such a composition with preferred self-bonding additives is to be found in Lampe et al. U.S. Pat. No. 3,888,815 which is hereby incorporated by reference.
Another type of silicone composition that cures to a silicone elastomer upon standing is a one-component RTV composition. Such a composition is packaged in the substantial anhydrous state in a one-component package. When it is desired to cure the composition, the seal on the package is broken, the composition is applied and upon exposure to atmospheric moisture, it cures to a silicone elastomer. Although the composition will cure to a silicone elastomer, both in a one-component and two-component type without the presence of the curing promoter that is the metal salt nevertheless the presence of the metal salt enhances the cure that is tighter cure at a faster period of time is obtained with a metal salt present. An example of such a composition is for instance to be found in Kulpa U.S. Pat. No. 3,296,161 which is hereby incorporated by reference. The Kulpa patent discloses a preferred self-bonding additive in the composition that is a diacyloxy, dialkoxy silane as the preferred self-bonding additive.
There are other examples of such one-component RTV compositions, however, such will not be gone into detail here. Basically these compositions differ from each other in the type of cross-linking agent, type of metal salt and the type of fillers and other ingredients such as self-bonding additives.
Recently silicone foams have gained attention in the area of fire protection. Thus, it has been found that silicone foams are desirable fire protection media for filling panels and partitions to enclose electrical components and other sensitive instruments so as to protect them from fire. Also, silicone foam has demonstrated a good capability for resisting the spread of fire and smoke in partitions that have been insulated with such silicone foam. Examples of silicone foam that can be utilized for these purposes are for instance to be found as disclosed in Smith U.S. Pat. No. 3,923,705 which is hereby incorporated by reference. Basically this patent discloses reacting a silanol containing polymer with a hydride polysiloxane in a presence of a platinum catalyst to produce flame resisting silicone foam. Also note the fact of the disclosure of the Smith patent that the ingredients react to equilibrate hydrogen gas which foams the silicone composition which then cures to a silicone foam. It is disclosed in that Smith application that part of the silanol polymer can be a vinylsiloxane. Also note the disclosure in the patent application of Modic U.S. Pat. Ser. No. 103,881 which is hereby incorporated by reference which discloses the utilization of a high vinyl content hydride polysiloxane platinum catalyzed composition to produce a silicone foam. This application is also incorporated by reference.
There have been also other developments in this area for instance Nitzsche et al. U.S. Pat. No. 3,050,485 which is hereby incorporated by reference which discloses the production of a silicone foam by reacting a silanol polymer with a hydride polysiloxane in the presence of a tin salt. Again, this composition generates hydrogen gas which is liberated from the composition when it foams. These systems disclosed above are particularly the Modic and Smith generate the foaming gas insitu in the composition upon the components being mixed together. The older method was to include a blowing agent in the composition which upon heating the composition would decompose the blowing agent which would liberate a gas which would foam the silicone composition to a silicone foam which would then be cured at the elevated temperatures by heat. For example see the disclosure of Modic U.S. Pat. No. 3,425,967 which is hereby incorporated by reference.
As the disclosure of the foregoing Modic Patent indicates an external blowing agent would suitably foam the silicone composition to a silicone foam. However, these types of foams had several problems. First of all, a suitable blowing agent had to be found. Second of all, the incorporation of such blowing agent into the composition as well the maintenance of the shelf stability of the composition effected the shelf stability of the composition.
A more advantageous system was the one disclosed in the foregoing Modic U.S. Pat. Ser. No. 103,881 which was disclosed above in that the blowing agent or blowing gas was generated insitu by the ingredients. The difficulty with such a composition was that it was still somewhat expensive even though it did not have an external blowing agent and depended on a very accurate and precise measurement of the different ingredients that went into the composition as well as the use of a solubilized platinum complex otherwise a suitable foam was not formed. In addition these compositions generate hydrogen gas as the blowing agent which was flammable and which in certain situations might create problems during the preparation and curing of the foam.
It should be noted that the Nitzsche et al. foam is not desirable in the applications envisioned by the present case that is for fire resistance applications in that the Nitzsche et al. foam is not a fire resistant foam. Accordingly, it was highly desirable to arrive at a simple, inexpensive method for producing silicone foams not only from expensive silicone compositions but also from the more simplier and cheeper silicone compositions such that a cheep and effective foam could be formed rapidly and with ease.
Accordingly, it is one object of the present invention to provide a simple and efficient method for mechanically foaming an SiH-olefin platinum catalyzed composition.
It is an additional object of the present invention to provide a simple and efficient method for mechanically foaming a two-component condensation curing RTV composition.
It is still an additional object of the present invention to provide a mechanical method for simply and efficiently foaming a condensation curing one-component RTV system.
These and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.